The oldest known Savior icon is this:
St. Catherine, Sinai, 6 c.
: This shows a full and rather thick beard, with characteristic tuft of hair right under the lower lip, giving way to a bear upper half of the chin.
This image, admittedly late-medieval (16c.) shows all elements of Christ's beard that prevail through the ages and, I believe came from eyewitness accounts.
Savior not made by hand
In addition to the bare upper chin on the St. Catherine image, we see long curls and the beard parting in two strands at the bottom.
These elements can be discerned, albeit with some difficulty, on the Shroud of Turin image:
